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Scroll Shell Temps

So I replaced 2 32hp scrolls in tandem yesterday. Ran the pumps overnight and charged her up today. Everything looked good. I did notice a slight oil leak at one of the rotolocks on the equalizer line. So I snugged it up and wiped it clean. Went through and checked SC, SH at compressors and at TXV's, amperages, oil levels, and discharge temps. All looked good. Cleaned up and thought...I should check that rotolock. It wasn't leaking, but I noticed the one fitting was warm. Actually the whole bottom of the compressor was warm.

So I'm thinking crankcase heater is running. Nope it's off. I measure 91 degrees at bottom of compressor. I check the other compressor bottom was 61 degrees. So I verify suction and discharge temps to each compressor. Suction temps are within 2 degrees at 59 degrees and discharge temps are with 3 degrees at 170 degrees. Oil level was 3/4 on the equalizer site glass. Again, I check shell temps and the one is alot warmer.

So I ran each compressor individuality and took readings. Readings looked good. The only thing that really changed was oil level in the equalizer sight, but with only one compressor running.....the oil sight on the equalizer doesn't really show true oil level in the running compressor. But the shells were close to suction temp.

With all my readings good, I let her run. I will be going back Saturday to replace cores and do an acid test. But it bothers me why the one compressor's shell is so warm, when both are running. Any one have an answer?

So I replaced 2 32hp scrolls in tandem yesterday. Ran the pumps overnight and charged her up today. Everything looked good. I did notice a slight oil leak at one of the rotolocks on the equalizer line. So I snugged it up and wiped it clean. Went through and checked SC, SH at compressors and at TXV's, amperages, oil levels, and discharge temps. All looked good. Cleaned up and thought...I should check that rotolock. It wasn't leaking, but I noticed the one fitting was warm. Actually the whole bottom of the compressor was warm.

So I'm thinking crankcase heater is running. Nope it's off. I measure 91 degrees at bottom of compressor. I check the other compressor bottom was 61 degrees. So I verify suction and discharge temps to each compressor. Suction temps are within 2 degrees at 59 degrees and discharge temps are with 3 degrees at 170 degrees. Oil level was 3/4 on the equalizer site glass. Again, I check shell temps and the one is alot warmer.

So I ran each compressor individuality and took readings. Readings looked good. The only thing that really changed was oil level in the equalizer sight, but with only one compressor running.....the oil sight on the equalizer doesn't really show true oil level in the running compressor. But the shells were close to suction temp.

With all my readings good, I let her run. I will be going back Saturday to replace cores and do an acid test. But it bothers me why the one compressor's shell is so warm, when both are running. Any one have an answer?

just curious in wich place was the original burnt compressor in?? The one reading 91 degree shell temp or the one reading 59 degrees???

This unit has three 15hp scrolls in tandem on circuit 1 and two 32hp scrolls in tandem on circuit 2. I lost both 32hp's on circuit 2 and replaced. So both are new.

The equalizer line goes across the two sight glasses. Upon removal of the old compressor, the oil level was just at the sight fitting. So with the replacements, I ended up only pulling 1 cup of oil out to match oil levels.

All my readings showed the compressors were happy and ok, but I just don't understand how the one compressor can have such a dramatic shell temperature difference. Especially giving that the suction pressure and temps are the same, oil level should be the same, and capacity should be the same.

I'm going there tomorrow to acid test oil and replace cores........I'll update what I find. There is another exact unit there. I'll check that as well.

Scrolls, can take up to 48hrs to bed in (some are better than others), it could be that the refrigerant flow passing through each compressor is different and that there may be a sight bit of back flow across the compression area. The compression part is still shifting the roughly the same mass of refrigerant, so power draw will be very similar, but the slight reduction in actual mass flow (suction port to discharge port), will cause less gas cooling of the compressor motor, so lifting the shell temp.
I have presumed that you are measuring a similar place and that the compressor suction superheat is high enough to ensure that there is no liquid entrapment into the suction stream.
Just one final one, listen carefully, can you hear a slight background whistle/woosh noise. The internal pressure relief valve could be passing ever so slightly. (similar results to bedding in).
So the time you get back, it should have bedded in, so would expect to see little difference. If still the big difference, run individually, check to see if the perform equally as good as each other "net cooling effect" if not, I would recommend as a "last resort", gently close the discharge valve until the internal relief blows (should remove any crap that maybe under the relief valve seat)

So a update....went Saturday to check cores and acid test. Acid test came clean. Liquid cores not too bad, but suction cores had a 12psi drop. Isolated cores. Installed pleats in suction. Liquid not pulling down. Wouldn't you know the factory liquid valve not holding. Shut down circuit.

Monday.....pulled all 170 pounds back out and replaced liquid valve. Ran pumps over night. Return the next day. Replaced liquid cores with some golds and gassed her back up. Again verified amperage, charge, and temps on both compressors.

With both compressors running for extended time.......the compressor on the right runs alot warmer shell temp then the other. Discharge temp, suction temp, and amperage are the same. So I setup the other condenser, at the location to run the same compressors. Same results. Right compressor runs alot warmer shell temps.

I left it as is. All my readings say the compressors are fine. But it just bothers me, I don't understand why the right side compressor's shell is warmer?